Agitator ball mills for the comminution of solid matter have been known for some time. In practice, they are used, virtually exclusively, for the so-called wet crushing process, i.e. the solid matter to be ground is comminuted in a suspension or dispersion with a liquid, e.g. water, solvent, binding medium or the like, and, in this connection, is simultaneously dispersed in the liquid. It has also already become known to use agitator ball mills in respect of a so-called dry crushing process, i.e. for a comminution of solid matter without the presence of a liquid. This has, however, not proved successful in practice.
From U.S. Pat. No. 3,311,310, an agitator ball mill is known which has a substantially vertically arranged cylindrical grinding container, in which is arranged, to be driven at high speed, a concentrically arranged agitator. The latter comprises an agitator shaft with substantially radially projecting agitating tools attached thereto, said tools being in the form of annular discs or agitating arms, or the like. The grinding chamber of this agitator ball mill is filled, for example, with sand as auxiliary grinding bodies or with corresponding auxiliary grinding bodies of glass, steel or any other suitable hard material, up to 75% of its clear volume. A grinding-stock suspension is pressed into the grinding chamber at the bottom end of the grinding container by means of a pump and leaves the grinding chamber at the top end, one it has passed through a grinding-stock/auxiliary-grinding-bodies separating device. The latter has a ring, which is attached to a lid of the grinding container, and a disc which rotates with the agitator shaft. A separating slot, the width of which is smaller than the diameter of the smallest auxiliary grinding bodies used and which becomes wider conically in an outward direction from the grinding chamber, is provided between said disc and the ring. The slot width is adjustable by the axial displacement of the disc relative to the ring. A separating device of this kind permits, in contrast to a simple screen or the like as the separating means, the grinding of grinding stock having a high viscosity, such as, for example, highly viscous printing inks, chocolate pastes, or the like. A so-called dry communication of solid matter is also not possible the case of these agitator ball mills, which can also be arranged horizontally or in any inclined intermediate position between vertical and horizontal. These known agitator ball mills are usually surrounded by a tempering jacket, which encloses the wall of the grinding chamber and which usually serves the purpose of cooling, i.e. to remove the energy introduced during grinding and converted into heat. It is precisely in the case of highly viscous grinding stock that the viscosity is very distinctly increased as the temperature is reduced. The consequence hereof is that, in the region of the grinding-chamber wall, due to the more intensive cooling there, a boundary layer of grinding stock having a particularly high viscosity builds up which, in turn, as a result of its insulating effect, impedes the conveying of heat from the grinding stock, which is disposed deeper in the interior of the grinding chamber, to the grinding-chamber wall, or, indeed, makes such conveying virtually impossible. This results in a restriction of the application possibilities of such agitator ball mills.
Agitator ball mills for use in the dry crushing of solid matter have become known. The basic structure of the agitator ball mill, namely a substantially vertically arranged grinding container and, arranged concentrically therein, an agitator means which can be driven at high speed, and a partial filling of the grinding chamber with auxiliary grinding bodies, has, in this regard, been retained. The solid matter to be comminuted is supplied to the grinding chamber from below by means of air, and leaves the grinding chamber at the top end, using the conveying action of the air current It has been found, in practical tests, that the residence time of the particles of solid matter to be comminuted in the grinding chamber is so wide-ranging that the result of grinding is completely unsatisfactory, since no adequately uniform particle fineness of the solid matter is achieved. In addition, the grinding stock settles on the grinding-chamber wall and results in a coating having a thickness such that there may be considerable interference in the operation of the mill.
An agitator ball mill having a slot-shaped grinding chamber has become known from U.S. Pat. No. 4,304,362. In this connection, a slot-shaped grinding chamber, which has a conical shape in its overall cross-section, is formed between a rotor and a stator. In this case, the auxiliary grinding bodies have rolling contact with the surface of the rotor or the grinding container. The auxiliary grinding bodies, in this instance, do not have free mobility. It is for this reason that dry crushing is impossible.
From German published patent application 35 36 454, an annular-passage ball mill for the continuous fine grinding of hard mineral material is known, in the case of which, in a closed grinding container is arranged a rotor, the outer surface of which defines a grinding slot together with the inner surface of the grinding container. Auxiliary grinding bodies are arranged in this grinding slot. The top part and the bottom part of the rotor taper in opposite directions. In this connection, not only the rotor, but also the grinding container, is provided with its own rotary drive. For the purpose of changing the grinding-slot width, the rotor or the grinding container can be displaced in a transverse direction relative to the central axis of rotor and grinding container, whereby a changeable eccentircity is achievable between rotor and grinding container. Here, too, a free mobility of the auxiliary grinding bodies is not ensured.
From German published examined patent application 12 23 236, an agitator ball mill of the generic kind is known, in the case of which the grinding container can be rotationally driven about the central longitudinal axis which is concentric with the agitator axis, in order to prevent, due to the centrifugal forces which are hereby exerted on the auxiliary grinding bodies, that they flow to a radially internally-located grinding-stock-discharge opening. The auxiliary grinding bodies are thereby largely deprived of the influence of the agitating tools, with the result that the grinding effect of this agitator ball mill is very slight. In the event of dry crushing, the grinding stock and the auxiliary grinding bodies would accumulate on the rotating inner wal of the grinding chamber, with the result that grinding stock and auxiliary grinding bodies would not execute any relative movements with respect to one another.
From U.S. Pat. No. 4,243,183, a preparation and comminution apparatus is known, which comprises a rotatable drum having rotors arranged therein This apparatus is used for the processing, preparation, mixing and comminution of voluminous, bulky, rough and hard materials. For this reason, the rotors support splitting tools which carry out an "impact-cracking" procedure of the materials to be comminuted. Brittle-fracturing materials are, in this regard, predominantly stressed by impact, whereas viscous materials are torn apart. In addition, balls may be introduced into this apparatus, the splitting tools of the rotors, in this case, serving as catapulting tools. In this regard, the balls render only a small comminution aid, in particular, by surface-impacting of the materials to be comminuted. Fine grinding, as is the case in agitator ball mills, is not possible in this instance.